The present invention relates to the lid and filter cage for a so-called wet/dry cannister or tank type vacuum cleaner, and is an improvement of the grid element construction disclosed in U.S. Pat. No. 4,185,974, issued Jan. 29, 1980 to K. R. Hiester for An Integral Filter Cage and Lid For Cannister Type Vacuum Cleaner.
Cannister or tank type vacuum cleaners are used for collecting various types of material, both dry and wet, and they are sometimes even used for collecting water or other liquids. In a typical vacuum cleaner of this type, the vacuum cleaner motor is supported on the removable lid for the dirt collecting tank and drives an impeller fan having an inlet side that communicates with the tank interior and draws a vacuum therein.
In the usual cannister vacuum cleaner, the lid is a generally flat surface disc or plate. To provide the lid with the strength needed for supporting the motor, especially while it is in operation, and for supporting an air filter assembly, the lid is typically formed of a strong, relatively rigid metal disc having a periphery that is shaped to sealingly engage the upper end of the side wall of the cylindrical tank. A hole is cut through the lid just beneath the mounting for the motor and this hole provides communication between the interior of the tank and the impeller fan driven by the motor.
A filter assembly is interposed between the interior of the tank and the inlet to the impeller fan for capturing particulate matter so that it does not escape into and past the fan and is not expelled from the vacuum cleaner. In the typical tank vacuum cleaner, directly beneath the lid of the tank and at the inlet to the impeller fan, there is a support for a replaceable filter element. Typically, the filter support is in the form of a generally cylindrical cage, and the filter element is in the form of a cylindrical annulus or sleeve of open cell foam material which is removably fitted over the filter cage. The annular sides of the filter cage are defined by vertical ribs, shaped and placed to support the surrounding filter element, yet spaced apart so as not to interfere with air flow. The bottom of the filter cage is closed off.
In situations where liquid or wet materials are being collected, it is necessary that the flow out of the tank and into the vacuum cleaner motor be halted before the liquid or wet material is drawn into the motor.
For supporting the particulate material filter element, the filter cage of the typical cannister vacuum cleaner is secured to the underside of the lid around the hole through the lid, and the filter cage is a molded plastic unit with an annular collar at its upper edge. Inside the filter cage, there is a ball or cylinder float element that sits on the base of the filter cage and is adapted to float up within the filter cage once the level of liquid in the tank rises above the bottom of the filter cage. The float element eventually floats high enough to seal the inlet to the impeller fan. Further operation of the vacuum cleaner is blocked until the tank is emptied of collected material. At the same time, the filter element may also be replaced.
As shown in the aforesaid U.S. Pat. No. 4,185,974, the bottom end of the filter cage is closed off by a bottom cover. An inlet grid element, including a grid covered opening, is disposed across the hole through the tank lid for permitting air to pass through the hole in the lid while also enclosing the top end of the filter cage as a safety feature to block access to the rotating impeller fan. A generally flat wall extends from the grid to the tank lid. The bottom edge of a sleeve extending downward from the grid constitutes a seat against which the float seals upon rising to a predetermined level.
If the fan continues to operate after its inlet is blocked by sealing of the float against the seat, the fan motor overheats. This causes the molded plastic grid unit to overheat at a time when there is an upward force transmitted through the float to the sleeve portion of the grid unit. As a result, the grid unit distorts, often resulting in a faulty sealing between the float and seat at the bottom edge of the sleeve.